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{{Short description|Date system of time since an epoch event}}
{{Use dmy dates|date=January 2020}}
{{Use American English|date=January 2025}}
{{Year in various calendars}}
{{Infobox calendar date today}}
A '''calendar era''' is the period of time elapsed since one ''[[epoch]]'' of a [[calendar]] and, if it exists, before the next one.<ref>{{Cite book| edition = 3| publisher = Univ Science Books| isbn = 978-1-891389-85-6| editor-first1 = Sean E. | editor-last1= Urban | editor-first2 = P. Kenneth | editor-last2 = Seidelmann | last1 = Richards | first1 = E. G.| title = Explanatory Supplement to the Astronomical Almanac| chapter = Calendars| location = Mill Valley, CA| date = 2013}}</ref> For example, the current year is numbered [[{{CURRENTYEAR}}]] in the Gregorian calendar, which numbers its years in the Western [[Christian era]] (the [[Coptic calendar#Coptic year|Coptic Orthodox]] and [[Ethiopian era|Ethiopian Orthodox]] churches have their own Christian eras).

In antiquity, regnal years were counted from the accession of a monarch. This makes the [[chronology of the ancient Near East]] very difficult to reconstruct, based on disparate and scattered king lists, such as the [[Sumerian King List]] and the Babylonian [[Canon of Kings]]. In East Asia, reckoning by [[era name]]s chosen by ruling monarchs ceased in the 20th century except for Japan, where they are still used.

==Ancient dating systems==

===Assyrian eponyms===
{{main|Eponym dating system}}

For over a thousand years, ancient [[Assyria]] used a system of [[Eponym dating system|eponyms]] to identify each year. Each year at the [[Akitu]] festival (celebrating the Mesopotamian new year), one of a small group of high officials (including the king in later periods) would be chosen by lot to serve as the ''[[limmu]]'' for the year, which meant that he would preside over the Akitu festival and the year would bear his name. The earliest attested ''limmu'' eponyms are from the Assyrian trading colony at [[Kültepe|Karum Kanesh]] in Anatolia, dating to the very beginning of the 2nd millennium BC,<ref>{{cite web|title=CDLI: The Old and Middle Assyrian limmu officials|url=http://cdli.ox.ac.uk/wiki/doku.php?id=list_of_old_assyrian_limmu_officials|website=Cuneiform Digital Library Initiative|access-date=18 May 2016|archive-date=12 November 2020|archive-url=https://web.archive.org/web/20201112025534/https://cdli.ox.ac.uk/wiki/doku.php?id=list_of_old_assyrian_limmu_officials|url-status=live}}</ref> and they continued in use until the end of the [[Neo-Assyrian Empire|Neo-Assyrian Period]], {{Circa|612 BC}}.

Assyrian scribes compiled ''limmu'' lists, including an unbroken sequence of almost 250 eponyms from the early 1st millennium BC. This is an invaluable chronological aid, because a solar eclipse was recorded as having taken place in the ''limmu'' of Bur-Sagale, governor of [[Tell Halaf|Guzana]]. Astronomers have identified this eclipse as [[Assyrian eclipse|one that took place on 15 June 763 BC]], which has allowed absolute dates of 892 to 648 BC to be assigned to that sequence of eponyms.<ref>{{cite book|last1=Millard|first1=Alan|title=The Eponyms of the Assyrian Empire, 910-612 BC (State Archives of Assyria Studies, Vol. 2)|date=1994|publisher=Neo-Assyrian Text Corpus Project|location=Helsinki|isbn=978-9514567155}}</ref> This list of absolute dates has allowed many of the events of the Neo-Assyrian Period to be dated to a specific year, avoiding the [[Chronology of the ancient Near East|chronological debates]] that characterize earlier periods of Mesopotamian history.

===Olympiad dating===
Among the ancient Greek historians and scholars, a common method of indicating the passage of years was based on the [[Ancient Olympic Games|Olympic Games]], first held in [[776 BC]]. The Olympic Games provided the various independent city-states with a mutually recognizable system of dates. Olympiad dating was not used in everyday life. This system was in use from the 3rd century BC. The modern Olympic Games (or Summer Olympic Games beginning 1896) do not continue the four year periods from ancient Greece: the 669th Olympiad would have begun in the summer of 1897, but the modern Olympics were first held in 1896.<ref name=Oxford>{{Cite book| edition = corrected printing| publisher = Oxford University Press| last1 = Blackburn| first1 = Bonnie| last2 = Holford-Strevens| first2 = Leofranc| title = The Oxford Companion to the Year| date = 2003 | isbn = 978-0-19-214231-3}}
</ref>{{rp|769}}

===Indiction cycles===
The [[indiction]] cycle was an agricultural tax cycle implemented in Roman Egypt. 15 indictions made up the cycle, an indiction being a year in duration. Documents and events began to be dated by the year of the cycle (e.g., "fifth indiction", "tenth indiction") in the 4th century, and this system was used long after the tax ceased to be collected. It was used in [[Gaul]], in [[Egypt]] until the [[Islamic conquest of Egypt|Islamic conquest]], and in the [[Eastern Roman Empire]] until its conquest in 1453.

A useful chart providing all the equivalents can be found in Chaîne's book on chronology,<ref>Chaîne, Marius. 1925. ''La chronologie des temps chrétiens de l’Égypte et de l’Éthiopie''. Paris: Librairie Orientaliste Paul Geuthner.</ref> and can easily be consulted online at the Internet Archive, from [[iarchive:lachronologiedes0000chan/page/134/mode/2up|page 134]] to [[iarchive:lachronologiedes0000chan/page/172/mode/2up|page 172]]. 

A rule for computing the indiction from an AD year number was stated by [[Dionysius Exiguus]]: add 3 and divide by 15; the remainder is the indiction, with 0 understood to be the fifteenth indiction.<ref name=Oxford/>{{rp|770}} Thus the indiction of  2001 was 9.<ref>{{cite book| author = Nautical Almanac Office of the [[United States Naval Observatory]] and [[Her Majesty's Nautical Almanac Office]] | date = 2000 | title = The Nautical Almanac for the year 2001 | location = Washington, DC | publisher = [[Government Printing Office]] | page = B2| bibcode = 2000naal.book.....N }}</ref> The beginning of the year for the indiction varied.<ref name=Oxford/>{{rp|769–71}}

===Seleucid era===
{{main|Seleucid era}}

The Seleucid era was used in much of the Middle East from the 4th century BC to the 6th century AD, and continued until the 10th century AD among Oriental Christians. The era is computed from the epoch 312 BC: in August of that year [[Seleucus I Nicator]] captured [[Babylon]] and began his reign over the Asian portions of [[Alexander the Great]]'s empire. Thus depending on whether the calendar year is taken as starting on 1 [[Tishri]] or on 1 [[Nisan]] (respectively the start of the Jewish civil and ecclesiastical years) the Seleucid era begins either in 311 BC (the Jewish reckoning) or in 312 BC (the Greek reckoning: October–September).

===Ancient Rome===

====Consular dating====
An early and common practice was Roman '[[Roman consul|consular]]' dating. This involved naming both [[Consul Ordinarius|''consules ordinarii'']] who had taken up this office on 1 January (since 153 BC) of the relevant civil year.<ref name=Oxford/>{{rp|6}} Sometimes one or both consuls might not be appointed until November or December of the previous year, and news of the appointment may not have reached parts of the Roman empire for several months into the current year; thus we find the occasional inscription where the year is defined as "after the consulate" of a pair of consuls.

The use of consular dating ended in AD 541 when the emperor [[Justinian I]] discontinued appointing consuls. The last consul nominated was [[Anicius Faustus Albinus Basilius]]. Soon afterwards, imperial regnal dating was adopted in its place.

====Dating from the founding of Rome====
Another method of dating was ''[[ab urbe condita]]'' (Latin for "from the founding of the city" of Rome) or {{lang|la|[[anno urbis conditae]]}} (Latin for "in the year of the founding of the city"), both abbreviated AUC.

Several epochs for this date were in use by [[Roman historiography|Roman historians]], all based on the incomplete surviving [[list of Roman consuls]] and the [[Roman mythology|myths]] of the [[Founding of Rome|city's founding]] by [[Romulus and Remus]]. The [[Varronian chronology|chronology]] established by [[Marcus Terentius Varro]] in the 1st century BC intercalated several years of [[dictator (Rome)|dictatorships]], a period of anarchy, and a standardized length of reign for all of Rome's [[list of kings of Rome|former kings]] to arrive at a year running from 754{{ndash}}753{{nbsp}}BC,<ref name=livius>{{citation |last=Lendering |first=Jona |contribution=Varronian Chronology |contribution-url=https://www.livius.org/articles/concept/varronian-chronology/ |date=2020 |title=''Official site'' |publisher=Livius |location=Amsterdam |url=https://livius.nl/ }}.</ref> taken as equivalent to the 3rd year of the 6th Olympiad. Because the [[Parilia]] had become associated with the founding of the city by his time, he took the specific date to have been 21 April 753{{nbsp}}BC. This became the official chronology of the empire by at least the time of [[Claudius]], who held [[Secular Games]] in AD 47 to celebrate the city's 800th anniversary. The 900th and 1000th anniversaries were then celebrated in 148 under [[Antoninus Pius]] and in 248 under [[Philip the Arab|Philip I]].

The AUC era was seldom used in the [[Roman calendar|traditional Roman]] or [[Julian calendar|early Julian calendars]]. Naming each year by its [[consul (Rome)|two consuls]] or by the emperor's regnal years predominated, with [[Hadrian]]'s [[aurei]]<ref>RIC II 144.</ref> and [[sestertii]] marking the [[Romaea]] in AUC 874 ({{smallcaps|ann dccclxxiiii nat vrb}}) a notable exception.<ref>{{citation |last=Raddato |first=Carole |location=[[Frankfurt am Main|Frankfurt]] |contribution-url=https://followinghadrian.com/2021/04/21/21-april-ad-121-hadrian-celebrates-romes-874th-birthday-with-circus-games-hadrian1900/ |contribution=21 April AD 121 {{mdash}} Hadrian Celebrates Rome's 874th Birthday with Circus Games |date=21 April 2021 |title=Following Hadrian |url=https://followinghadrian.com }}.</ref> AUC dating became more common in late antiquity, appearing in [[Censorinus]], [[Paulus Orosius|Orosius]], and others. During the early Middle Ages, some church officials like [[Boniface IV]] employed AUC and AD dating together.{{Citation needed|date=December 2007|reason='although it occurs occasionally in papal documents of the time of John XIII (965–972), it was not the rule before the twelfth century': http://www.newadvent.org/cathen/04636c.htm - and that's not even about using abbreviations}}

Historical Roman dating employed several different dates for the beginning of the year. Modern application of the AUC era generally ignores this, the known mistakes<ref name=livius/> in Varro's own calculations, and the 752{{nbsp}}BC epoch used by the [[Fasti Capitolini|Fasti]] and later Secular Games, such that AD {{CURRENTYEAR}} is generally considered equivalent to AUC {{#expr: {{CURRENTYEAR}}+753}} ({{CURRENTYEAR}} + 753).

====Regnal years of Roman emperors====
Another system that is less commonly found than might be thought was the use of the [[regnal year]] of the [[Roman emperor]]. At first, [[Augustus]] indicated the year of his reign by counting how many times he had held the office of consul, and how many times the [[Roman Senate]] had granted him the [[tribunicia potestas|power of a tribune]] ({{langx|la|tribunicia potestas}}, abbr. TRP), carefully observing the fiction that his powers came from these offices granted to him, rather than from his own person or the many [[Roman legion|legion]]s under his control. His successors followed his practice until the memory of the [[Roman Republic]] faded (about AD 200), when they began to use their regnal year openly.

====Dating from the Roman conquest====
Some regions of the [[Roman Empire]] dated their calendars from the date of Roman conquest, or the establishment of Roman rule.

The [[Spanish era]], or the Era of [[Julius Caesar|Caesar]], counted the years from [[38 BC]] and, although the exact reasons for this are unknown, it is usually attributed to either the levy of a general tax from the known world by [[Augustus|Octavian]] or the end of the roman conquest of the peninsula during the civil war of the [[Second Triumvirate]]. Either way the date traditionally marks the establishment of Roman rule in Spain and was used in official documents by the [[Kingdom of the Suebi|Suebian]] and [[Visigothic Kingdom|Visigothic kingdoms]] and later in [[Kingdom of Portugal|Portugal]], [[Kingdom of Aragon|Aragon]], [[Kingdom of Valencia|Valencia]], [[Crown of Castile|Castile]], and [[southern France]]. This system of calibrating years fell to disuse in the Early Modern Age and was replaced by today's ''Anno Domini''.<ref>Gedaliah ibn Jechia the Spaniard, ''Shalshelet Ha-Kabbalah'', Jerusalem 1962, p. 271 (Hebrew)</ref> The months and years are the same as the [[Julian calendar|Julian Calendar]].

Throughout the Roman and Byzantine periods, the [[Decapolis]] and other Hellenized cities of Syria and Palestine used the [[Pompeian era]], counting dates from the Roman general [[Pompey]]'s conquest of the region in 63 BC.

===Maya===
A different form of [[Maya calendar]] was used to track longer periods of time, and for the inscription of calendar dates (i.e., identifying when one event occurred in relation to others). This form, known as the [[Mesoamerican Long Count calendar|Long Count]], is based upon the number of elapsed days since a mythological starting-point. According to the calibration between the Long Count and Western calendars accepted by the great majority of Maya researchers (known as the GMT correlation), this starting-point is equivalent to 11 August, 3114 BC in the proleptic Gregorian calendar or 6 September in the Julian calendar (−3113 astronomical).

===Other dating systems===
A great many local systems or [[era]]s were also important, for example the year from the foundation of one particular city, the regnal year of the neighboring [[History of Persia|Persian emperor]], and eventually even the year of the reigning [[Caliph]].

==Late Antiquity and Middle Ages==
Most of the traditional calendar eras in use today were introduced at the time of transition from [[Late Antiquity]] to the [[Early Middle Ages]], roughly between the 6th and 10th centuries.

===Christian era===
*The ''[[Etos Kosmou]]'' of the [[Byzantine Calendar]] commences with the [[dating creation|creation of the world]] portrayed in [[Book of Genesis|Genesis]], the date of which- arrived at by the monk Giorgios- being 1 September, 5509 BC. Its first known use occurred in the 7th century AD, although its precursors were developed about AD 400.
*The [[Era of Martyrs]] or Era of Diocletian is reckoned from the beginning of the reign of Roman Emperor [[Diocletian]]; the first year of this era was 284/5. It was not the custom to use regnal years in Rome, but it was the custom in Roman Egypt, which the emperor ruled through a prefect (the king of Egypt). The year number changed on the first day of the Egyptian month [[Thoth]] (29 August three years out of four, 30 August the year before a Roman leap year.) Diocletian abolished the special status of Egypt, which thereafter followed the normal Roman calendar: consular years beginning on 1 January. This era was used in the Easter tables prepared in Alexandria long after the abdication of Diocletian, even though Diocletian was a notorious persecutor of Christians. The Era of Diocletian was retained by the [[Coptic calendar|Coptic Church]] and used for general purposes, but by 643 the name had been changed to Era of the Martyrs.<ref name=Oxford/>{{rp|766–7}}
*The [[Ethiopian calendar#Incarnation Era|Incarnation Era]] is used by [[Ethiopia]]. Its epoch is 29 August, AD 8 in the Julian calendar.
*The [[Armenian calendar]] has its epoch fixed at AD 552.

====Dionysian "Common Era"====
{{Main|Anno Domini|Common Era}}

The era based on the [[Incarnation (Christianity)|Incarnation]] of [[Christ]] was introduced by [[Dionysius Exiguus]] in 525 and is in continued use with various reforms and derivations. The distinction between the Incarnation occurring with the [[Annunciation|conception]] or the [[Nativity of Jesus]] was not drawn until the late ninth century.<ref name=Oxford/>{{rp|881}} The first day of the numbered year varied from place to place and depended on the calendar in use: when, in 1600, Scotland adopted 1 January as the first day of the year, this was already the case in much of continental Europe. England adopted this practice in 1752.<ref name=Oxford/>{{rp|7}}

* A.D. (or AD) – for the [[Latin]] ''[[Anno Domini]]'', meaning "in the year of (our) Lord". This is the dominant or Western Christian Era; AD is used in the Gregorian calendar. ''[[Anno Salutis]]'', meaning "in the year of salvation" is identical. Originally intended to number years from the Incarnation of [[Jesus]], according to modern thinking the calculation was a few years off. Years preceding AD 1 are numbered using the BC era, avoiding zero or negative numbers. AD was also used in the Christianized [[Julian calendar]], but the first day of the year was either 1 March, [[Easter]], 25 March (Feast of the Annunciation), 1 September, or 25 December (Feast of the Nativity), not 1 January. To distinguish between the Julian and Gregorian calendars, ''O.S.'' and ''N.S.'' were often added to the date, especially during the 17th and 18th centuries, when both calendars were in common use. [[Old Style and New Style dates|Old Style]] (O.S.) was used for the Julian calendar and for years not beginning on 1 January. [[Old Style and New Style dates|New Style]] (N.S.) was used for the Gregorian calendar and for Julian calendar years beginning on 1 January. Many countries switched to using 1 January as the start of the numbered year at the same time as they switched from the Julian calendar to the Gregorian calendar, but others switched earlier or later.
* B.C. (or BC) – meaning "Before Christ". Used for years before AD 1, counting backwards so the year ''n'' BC is ''n'' years before AD 1. Thus there is no [[year zero|year 0]].
* C.E. (or CE) and B.C.E. (or BCE)  – meaning "[[Common Era]]" and "Before the Common Era", numerically equivalent to AD and BC, respectively (in writing, "AD" ''precedes'' the year number, but "CE" ''follows'' the year: AD 1 = 1 CE.)<ref>{{cite book | title =Associated Press Stylebook | date = 2007 | location = New York | publisher = Basic Books | page = 6 | isbn = 978-0-465-00489-8}}. "Because the full phrase would read ''in the year of the Lord 96'', the abbreviation A.D. goes before the figure for the year: ''A.D. 96.''"</ref> The  Latin equivalent ''vulgaris aera'' was used as early as 1615  by [[Johannes Kepler]].<ref>A 1635 English edition of that book has the title page in English – so far, the earliest-found usage of "Vulgar Era" in English. The English phrase "common Era" appears at least as early as 1708.{{citation needed|date=May 2018}}
In Latin, "Common Era" is written as ''Vulgaris Aera''. It also occasionally appears as ''æra vulgaris'', ''aera vulgaris'', ''anni vulgaris'', ''vulgaris aera Christiana'', and ''anni vulgatae nostrae aerae Christianas''.</ref> The English abbreviations C.E. and B.C.E. were introduced in the 19th century  by Jewish intellectuals, wishing to avoid the abbreviation for ''dominus'' "lord" in implicit reference to Christ.<ref>Use of "C.E." and "B.C.E.": [[Morris Jacob Raphall]]. ''Post-Biblical History of The Jews'' (1856). 
Explicit use of "b.c.e." for "before the common era": 
Max Stern, ''Lemaʼan Yilmedu: A Second Hebrew Reader for Jewish Schools and Private Instruction'' (1881), p. 37.</ref> By the later 20th century, the abbreviations had come into wider usage by authors who wished to emphasize [[secularism]].<ref>{{cite book | first1 = John | last1 = Sumser | title = The Conflict Between Secular and Religious Narratives in the United States: Wittgenstein, Social Construction, and Communication | date = 2016 | url = https://books.google.com/books?id=5SFsDAAAQBAJ&pg=PA69 | page = 69 | isbn = 9781498522090 | access-date = 2 October 2020 | archive-date = 18 January 2021 | archive-url = https://web.archive.org/web/20210118090442/https://books.google.com/books?id=5SFsDAAAQBAJ&pg=PA69 | url-status = live }}</ref>

=====Dionysian-derived=====
* [[Astronomical year numbering]] situates its year 0 with 1 BC, and counts negative years from 2 BC backward (−1 backward), so 100 BC is −99.
* The [[Holocene calendar|human era]], also named Holocene era, proposed by [[Cesare Emiliani]] adds 10,000 to AD years, so that AD 1 would be the year 10,001.<ref>{{cite journal |last1=Cesare |first=E. |date=1993 |title=Calendar reform |url=https://www-nature-com.insu.bib.cnrs.fr/articles/366716b0 |department=Correspondence |journal=Nature |volume=336 |page=716}}</ref>
* ''[[Anno Lucis]]'' of [[Freemasonry]] adds 4000 years to the AD year.

===Islamic===
*[[Anno Hegirae|A.H.]] (or AH) for the Latinized ''[[Anno Hegirae]]'', meaning "in the year of the [[Hijra (Islam)|Hijra]]", [[Muhammad]]'s emigration from Mecca to Medina in September 622, which occurred in its first year, is used in the [[Islamic calendar]]. Since the Islamic calendar is a purely [[lunar calendar]] of about 354 or 355 days, its year count increases faster than that of [[solar calendar|solar]] and [[lunisolar calendar]]s.
*[[Solar Hijri calendar|S.H.]] (or SH){{Citation needed|date=September 2007}} is used by the [[Iranian calendar]] to denote the number of ''solar'' years since the Hijra. The year beginning at the vernal equinox equals the number of the Gregorian year beginning at the preceding 1 January minus 621.

===Hindu===
*[[Hindu calendar]], counting from the start of the [[Kali Yuga]], with its epoch on 18 February, 3102 BC Julian (23 January, 3102 BC Gregorian), based on Aryabhata (6th century).
*[[Vikrama Samvat]], 56-57 BC, introduced about the 12th century.
*[[Saka Era|S.E.]] or (SE) – for the [[Shaka era|Saka Era]], used in some [[Hindu calendar]]s and in the [[Indian national calendar]], with an epoch near the vernal equinox of year 78 (its year 0); its usage spread to Southeast Asia before year 1000. This era is also used (together with the Gregorian calendar) in the Indian national calendar, the official civil calendar used in communiques issued by the Government of India.
*[[Lakshmana Era]], established by the [[Bengal]]i ruler [[Lakshmana Sena]] with an epoch of 1118–1119. It was used for at least 400 years in Bihar and Bengal.

===Southeast Asia===
The Hindu Saka Era influences the calendars of southeast Asian [[Greater India|indianized kingdom]]s.
*[[Buddhist calendar|B.E.]] – for the [[Buddhist calendar|Buddhist Era]], introduced by [[Vajiravudh]] in 1912, which has an [[epoch (reference date)|epoch]] (origin) of 544 BC. This year is called year 1 in [[Sri Lanka]] and [[Burma]], but year 0 in [[Thailand]], [[Laos]] and [[Cambodia]]. Thus the year 2500 B.E. occurred in 1956 in the former countries, but in 1957 in the latter. In Thailand in 1888 King [[Chulalongkorn]] decreed a National Thai Era, dating from the founding of [[Bangkok]] on 6 April 1782. In 1912 New Year's Day was shifted to 1 April. In 1941 Prime Minister [[Plaek Pibulsonggram|Phibunsongkhram]] decided to count the years since 543 BC. This is the [[Thai solar calendar]] using the Thai Buddhist Era aligned to the western solar calendar.
*'''BE''' for Burmese Era – from [[Burmese calendar]] originally with an epochal year 0 date of 22 March 638; from which derived '''CS''' for [[Chula Sakarat]] era; variously known as '''LE''' Lesser Era; '''ME''' Minor Era – the Major or Great Era being the [[Saka Era]] of the [[Indian national calendar]]
:B.E. of the Bahá'í calendar is below.

===Bahá'í===
*[[Bahai calendar|B.E.]] – The [[Bahá'í calendar]] dates from the year of the declaration of the [[Báb]]. Years are counted in the Bahá'í Era (BE), which starts its year 1 from 21 March 1844.

===Jewish===
*[[Anno Mundi|A.M.]] (or AM) – for the Latin ''[[Anno Mundi]]'', meaning "in the year of the world", has its epoch in the year 3761 BC. This was first used to number the years of the modern [[Hebrew calendar]] in 1178 by [[Maimonides]]. Precursors with epochs one or two years later were used since the 3rd century, all based on the [[Seder Olam Rabba]] of the 2nd century. The year beginning in the northern autumn of 2000 was 5761 AM.

===Zoroastrian===
*The [[Zoroastrian calendar]] used regnal years since the reform by [[Ardeshir I]], but after the fall of the [[Sassanid Empire]], the ascension of the last Sassanid ruler, [[Yazdegerd III of Persia]], crowned 16 June 632, continued to be used as the reference year, abbreviated [[Yazdegerd era|Y.Z.]] or "Yazdegerd era".

==Modern==
{{main|List of calendars}}

===Political===
*The Republican Era of the [[French Republican Calendar]] was dated from 22 September 1792, the day of the proclamation of the [[French First Republic]]. It was used in Revolutionary France from 24 October 1793 (on the Gregorian calendar) to 31 December 1805.
*The [[Positivist calendar]] of 1844 takes 1789 as its epoch.
*The [[Minguo calendar|Republican era]] is used by the [[Republic of China]] (now usually known as "Taiwan") since 1912, which is the first year of the republic. Coincidentally, this is the same as the [[Juche#Calendar|Juche era]] used in [[North Korea]], the year of the birth of its founder [[Kim Il-Sung]].
* The [[Era Fascista]] 'Fascist Era' was instituted by the [[Fascism|Italian Fascists]] and used [[Roman numerals]] to denote the number of years since the [[March on Rome]] in 1922. Therefore, 1934, for example, was XII E.F. (''era fascista''). This era was abolished with the fall of fascism in Italy on 25 July 1943, but restored in the northern part of the country during the [[Italian Social Republic]]. The Gregorian calendar remained in simultaneous use and a double numbering was adopted: the year of the [[Common era]] was presented in Arabic numerals and the year of the fascist era in Roman numerals. The year of the Fascist calendar began on 29 October, so, for example, 27 October 1933 was XI E.F. but 30 October 1933 was XII E.F.
*China traditionally reckoned by the regnal year of its emperors, see [[Chinese era name]]. Most Chinese do not assign numbers to the years of the [[Chinese calendar]], but the few who do, like expatriate Chinese, use a continuous count of years from the reign of the legendary [[Yellow Emperor]], using 2698 BC as year 1. Western writers begin this count at either 2637 BC or 2697 BC (see [[Chinese calendar#Beginnings|Chinese calendar]]). Thus, the Chinese years 4637, 4697, or 4698 began in early 2000.
*In Korea, from 1952 until 1961 years were numbered via ''[[Dangun#Dating|Dangi]]'' years, where 2333 BC was regarded as the first such year.
*The [[Assyrian calendar]], introduced in the 1950s, has its era fixed at 4750 BC.
*The [[Japanese calendar]] dates from the accession of the current [[Emperor of Japan]]. The current emperor took the throne in May 2019, which became Reiwa 1, and which was until then Heisei 31.
*The [[United States]] government sometimes uses a calendar of the era of its [[Independence Day (United States)|Independence]], fixed on 4 July 1776, together with the ''Anno Domini'' civil calendar. For instance, its [[U.S. Constitution|Constitution]] is dated "the Seventeenth Day of September in the Year of our Lord one thousand seven hundred and Eighty seven and of the Independence of the United States of America the Twelfth."<ref>{{Cite web |url=https://www.archives.gov/exhibits/charters/constitution_transcript.html |title=U.S. Constitution |access-date=25 August 2017 |archive-date=19 August 2011 |archive-url=https://web.archive.org/web/20110819235454/http://www.archives.gov/exhibits/charters/constitution_transcript.html |url-status=live }}</ref> [[Presidential proclamation (United States)|Presidential proclamations]] are also dated in this way.<ref>{{Cite web| title = Presidential Actions| website = The White House| location = Washington, DC| access-date = 2020-01-11| url = https://www.whitehouse.gov/presidential-actions/| archive-date = 18 January 2021| archive-url = https://web.archive.org/web/20210118041804/https://www.whitehouse.gov/presidential-actions/| url-status = live}}</ref>

===Religious===
*[[Dianetics: The Modern Science of Mental Health#Role in Scientology|A.D.]] – "After [[Dianetics]]". In [[Scientology]], years are numbered relative to the first publication of the book ''[[Dianetics: The Modern Science of Mental Health]]'' (1950).<ref name="LATcostly">{{cite news | last1 = Sappell | first1 = J. | last2 = Welkos | first2 = R. W. | date = 28 June 1990 | url = http://www.latimes.com/news/local/la-scientology062890,0,6570814.story | title = Costly Strategy Continues to Turn Out Bestsellers | newspaper = Los Angeles Times | access-date = 25 December 2011 | archive-date = 27 October 2013 | archive-url = https://web.archive.org/web/20131027185121/http://www.latimes.com/news/local/la-scientology062890,0,6570814.story | url-status = live }}</ref>
*[[Discordian calendar|Y.O.L.D.]] – In the [[Discordian calendar]], the standard designation for the year number is YOLD (Year of [[Eris (mythology)|Our Lady of Discord]]). The calendar begins counting from 1 January 1166 BC in the [[Discordian]] year 0, ostensibly the date of origin of the [[Greyface|Curse of Greyface]]. An alternate designation, A.D.D. has been occasionally seen (Anno Domina Discordia, a Latin translation of YOLD, but presumably also a play on [[attention deficit disorder]]).{{citation needed|date = May 2022}}
*e.v. – ''Era vulgaris''. (From Latin, meaning "common era", usually stylized in lowercase.) Used by some followers of [[Aleister Crowley]] to designate the era from the [[Thelemic]] calendar which is used by some Thelemites to designate a number of years since Crowley's inauguration of the so-called [[Aeon (Thelema)#Aeon of Horus|Aeon of Horus]], which occurred on 20 March 1904, and coincides with both the Thelemic new year and a holiday known as the Equinox of the Gods. The abbreviation "A.N.", for ''Aerae Novae'' ("New Era" in Latin), is also used for dates in the Thelemic calendar.{{citation needed|date = May 2022}}

===Practical===
*[[Before Present|B.P.]] – for [[Before Present]], specifically, the number of [[radiocarbon dating|radiocarbon]] years before 1950.
*[[Julian day number]] – for counting days, not years, its era fixed at noon 1 January, 4713 BC in the [[proleptic Julian calendar]]. This equals 24 November, 4714 BC in the [[proleptic Gregorian calendar]]. From noon of this day to noon of the next day was day 0. Multiples of 7 are Mondays. Negative values can also be used. Apart from the choice of the zero point and name, this Julian day and Julian date are not related to the [[Julian calendar]]. It does not count years, so, strictly speaking, it has no era, but it does have an [[epoch (reference date)|epoch]]. Today (noon-to-noon UTC) the value is {{#expr:({{CURRENTJULIANDAY}}-0.5) round 0}}.
* [[Unix time]] – for counting elapsed seconds since the [[Unix epoch]] set at 00:00:00 or midnight UTC of 1 January 1970, though there are problems with Unix implementation of [[Coordinated Universal Time]] (UTC).
* [[Holocene calendar]]

==See also==
* [[Calendar reform]]
* [[Common Era]]
* [[Julian day]]
* [[List of calendars]]

==References==
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[[Category:Chronology]]